In a number of medical uses, a product is adhered directly to the skin, such as in the case of a wound dressing or an ostomy skin barrier. Such a product must be securely affixed to the skin to keep it in place and must absorb whatever fluid is produced under or near it, such as perspiration, wound exudate, fluid fecal matter, and the like.
Wound dressings typically perform several functions to facilitate healing. These functions include absorbing wound exudate, regulating pH to create an optimal healing environment and reduce microbial activity, and protecting the wound from infection. Many such wound dressings are self-adhesive and contain an adhesive layer that typically adheres to the peri-wound skin of a wearer. It is known that skin often becomes irritated under wound dressings.
Known wound dressings achieve the aforementioned functionality through the use of several individual components. For example, known dressings often use hydrocolloids, e.g., carboxymethylcellulose (CMC), pectin, or gelatin, to absorb wound exudate. While some hydrocolloids are also capable of independently adjusting pH, the degree of pH buffering they can provide is limited by the amount of available hydrocolloid in the dressing, which, in turn, is dependent on the desired fluid handling properties of the dressing. Moreover, the buffering effect of hydrocolloids alone is not optimal.
Additionally, appropriate levels of both absorption and pH control are often difficult to achieve simultaneously. A certain extent of absorption by the wound dressing is required for pH control and is generally desirable in a wound dressing. However, the absorption of an excessive amount of fluid can cause an undesirable amount of swelling of the wound dressing, leading to distension and possible loss of adhesion. In certain instances, absorption of an excessive amount of fluid can cause dissolution of the adhesive composition, which is also highly undesirable.
Adhesive compositions containing hydrocolloids are well known, as disclosed, for example, in U.S. Pat. Nos. 5,571,080, 3,339,546, 4,192,785, 4,296,745, 4,367,732, 4,813,942, 4,231,369, 4,551,490, 4,296,745, 4,793,337, 4,738,257, 4,867,748, 5,059,169, and 7,767,291, the disclosures of which are incorporated herein by reference. Hydrocolloids are commonly used in what is commonly referred to as hydrocolloid skin barriers or hydrocolloid wound dressings. Such skin barriers and wound dressings normally include a water-insoluble pressure-sensitive adhesive as a continuous phase with particles of one or more hydrocolloids dispersed throughout the adhesive as a liquid-absorbing and swellable discontinuous phase.
The water-insoluble adhesive phase of commercial skin barriers and wound dressings typically consists of polyisobutylene (PIS), or block copolymers such as styrene-isoprene-styrene (SIS), or blends of these materials. The surface tack may be modified by the addition of tackifier components.
Patients with a permanent or temporary ostomy (colostomy, ileostomy, and the like) have need of a pouch to contain the expelled fecal material or urine. The pouch is normally attached to the peristomal skin with an adhesive skin barrier that attaches the pouch to the skin and absorb liquids flowing from the stoma or produced by the peristomal skin. A skin barrier is normally replaced every three to five days but may remain in place for up to a week. During use of the barrier, the peristomal skin may become irritated due to prolonged contact with the fecal material. Over time, the irritation can become severe.
In some applications, an ostomy skin barrier has an adhesive tape border around its periphery for additional security. The adhesive for said border is typically an acrylic adhesive. As used herein, the term “skin barrier” is intended to include any skin barrier either with or without an adhesive tape border.
Both wound exudate and fecal material contain proteolytic and lipolytic enzymes. These enzymes, when contained in a closed, moist environment, are thought to degrade the stratum corneum and contribute to the observed irritation. Moreover, since both wound dressings and ostomy skin barriers are normally removed and re-applied on a regular basis, the integrity of the skin under them becomes compromised and more susceptible to irritation than normal skin.
Normal skin has a so-called “acid mantle” which maintains the surface of the skin at a pH typically between about 4.0 and 5.5 (slightly acidic). This pH range promotes the growth of beneficial microorganisms and retards the growth of harmful microorganisms, while helping to maintain the integrity of the skin. At this pH level, the activity of (and hence the damage caused by) the proteolytic and lipolytic enzymes from wound exudate or fecal matter would not be severe. However, the wound exudate and stomal fluid normally have a pH in the range of 6.0 to 8.0. This increase in pH over the normal skin pH causes a significant increase in the activity of the enzymes and hence in their ability to cause irritation.
As for wound dressings, appropriate levels of both absorption and pH control are often difficult to achieve simultaneously for ostomy skin barriers. A certain extent of absorption by the skin barrier is required for pH control and is generally desirable. However, the absorption of an excessive amount of fluid can cause an undesirable amount of swelling of the skin barrier, leading to distension and possible loss of adhesion. In certain instances, absorption of an excessive amount of fluid can cause dissolution of the adhesive composition, which is also highly undesirable.
Current skin barriers incorporating hydrocolloids such as pectin and CMC have only limited pH buffering capacity. When exposed to water or saline solution, they are capable of adjusting pH to a level in the desired range from about 4.0 to 5.5. However, it is important to note that physiological fluids such as stoma output or wound exudates are also buffered, typically at pH levels close to neutral. When current skin barriers are exposed to such fluids, the strong buffering capacity inherent in the physiological fluid overwhelms the weak buffering capacity of the skin barrier. As a result, the pH at the surface of the skin barrier increases to approach the pH of the fluid used to challenge the skin barrier. Thus, it would be desirable to provide a skin barrier with enhanced pH buffering capacity. It would also be desirable to provide a skin barrier with optimal absorption characteristics.
In view of the above, it would be desirable to have an adhesive composition containing a suitable buffer to maintain the pH of the skin under a wound dressing or a stomal skin barrier or the like product at about 4.0 to about 5.5 without being inherently irritating to the user's skin, and which would have an optimal extent of fluid absorption.